1. Field of the Invention
The present invention relates to a semiconductor design technology and, more particularly, to an embedded system having a processor and a memory and a method for relocating memory pages in the embedded system.
This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and/or the Korean Institute for Information Technology Advancement (IITA) [2006-S-048-01, “embedded DSP platform for processing audio and video signal”].
2. Description of Related Art
The development of an information technology (IT) makes portable devices popular. Various types of portable devices have been commonly used in daily life, lately. Since the portable devices are driven by batteries, there have been many researches in progress for extending an operation time of a portable device with a limited battery capacity. In order to extend the operation time, a technology for minimizing power consumption of semiconductor chips in a portable device was introduced. The technology became a factor to decide the productivity of the portable device.
The power consumption of a semiconductor chip may be divided into two factors, dynamic power consumption and leakage power. The dynamic power consumption denotes electric power consumed by a transistor in a semiconductor and a capacitor component in a metal line. The capacitor component is filled up with charge and emptied repeatedly at every clock cycle. Since the flow of charge is current, it is the major factor of the power consumption. Meanwhile, further the semiconductor manufacturing process is advanced, more the leakage power occurs. That is, a gate oxide thickness becomes thinner as the semiconductor manufacturing process is advanced. Since thin gate oxide cannot stand high voltage, it is required to lower the operating voltage of a semiconductor circuit. The lowered operating voltage becomes closer to a threshold voltage and thus a transistor is not completely turned off or on. As a result, the amount of current (sub-threshold current) abruptly increases generated under the threshold voltage.
In order to reduce the dynamic power consumption, a method for interrupting the clock of a processor, a method for reducing the number of gates, and a method for reducing the number of signal transitions in a circuit were introduced. However, these methods cannot reduce the leakage current. The most effective method for interrupting the leakage current is to cut off the power of a circuit.
If the power of a circuit is cut off, the circuit does absolutely not operate. In case of a Flip-flop or a memory, memorized data is lost if the power is cut off. The power cut off method may be acceptable if an entire embedded system operates in a power down mode. However, it is very rare to operate the entire embedded system in the power down mode. Therefore, a method for cutting off power of a predetermined part was introduced. As a method for cutting off power in a transistor level, a variable threshold circuit, a dual-threshold transistor, a multi-threshold transistor, and a power gating structure were introduced.
In order to effectively cut off the leakage current, it is more effective to use a method for dynamically controlling power of circuit divisions in a system rather than using of a new designed transistor circuit. Particularly, the number of gates of a memory occupies much more weight than the number of logic gates because the large capacity memory is integrated in a multimedia based embedded system. Therefore, the reduction of leakage current generated in a memory critically influences to the reduction of overall power consumption.